Idk where to put this on glow workplace harrasment

Ja

Ok so i have two woman of the same race a different race of myself ganging up on me in my classroom they try to get me alone and talk bad about me to each other in front of me or they try to say mean things and upset me. They make hand gestures and bad looks. Bump into me and wait by my car just to stare me down. My manager says I have to write a letter to HR. What would you do in this situation?